Devices for imaging body cavities or passages in vivo are known in the art and include endoscopes and autonomous encapsulated cameras. Endoscopes are flexible or rigid tubes that pass into the body through an orifice or surgical opening, typically into the esophagus via the mouth or into the colon via the rectum. An image is formed at the distal end using a lens and transmitted to the proximal end, outside the body, either by a lens-relay system or by a coherent fiber-optic bundle. A conceptually similar instrument might record an image electronically at the distal end, for example using a CCD or CMOS array, and transfer the image data as an electrical signal to the proximal end through a cable. Endoscopes allow a physician control over the field of view and are well-accepted diagnostic tools. However, they do have a number of limitations, present risks to the patient, are invasive and uncomfortable for the patient, and their cost restricts their application as routine health-screening tools.
Because of the difficulty traversing a convoluted passage, endoscopes cannot reach the majority of the small intestine and special techniques and precautions, that add cost, are required to reach the entirety of the colon. Endoscopic risks include the possible perforation of the bodily organs traversed and complications arising from anesthesia. Moreover, a trade-off must be made between patient pain during the procedure and the health risks and post-procedural down time associated with anesthesia. Endoscopies are necessarily inpatient services that involve a significant amount of time from clinicians and thus are costly.
An alternative in vivo image sensor that addresses many of these problems is capsule endoscope. A camera is housed in a swallowable capsule, along with a radio transmitter for transmitting data, primarily comprising images recorded by the digital camera, to a base-station receiver or transceiver and data recorder outside the body. The capsule may also include a radio receiver for receiving instructions or other data from a base-station transmitter. Instead of radio-frequency transmission, lower-frequency electromagnetic signals may be used. Power may be supplied inductively from an external inductor to an internal inductor within the capsule or from a battery within the capsule.
An autonomous capsule camera system with on-board data storage was disclosed in the U.S. patent application Ser. No. 11/533,304, entitled “In Vivo Autonomous Camera with On-Board Data Storage or Digital Wireless Transmission in Regulatory Approved Band,” filed on Sep. 19, 2006. This application describes a motion detection that is conducted using a portion of each image, the portion being stored in a partial frame buffer. In one embodiment, two partial frame buffers are used as operand buffers for a reduced version of a current image and a reference image, respectively. The reference frame buffer corresponds to the one containing a previously stored or transmitted digital image. When the image in the operand partial frame buffer is determined not to be stored, that partial frame buffer may be overwritten by the next digital image to be motion-detected. Otherwise, the operand partial frame buffer would be designated the next reference partial frame buffer, and the current reference partial frame buffer is designated the next operand partial frame buffers. In the above application, a metric for measuring the degree of motion between the two partial images described and is used to compare with a threshold as to whether to capture an underlying image or as to determine a proper compression ratio for the underlying image.
The U.S. patent application Ser. No. 11/623,601, entitled “Lighting Control for In Vivo Capsule Camera” describes methods and systems to adjust light source illumination based on image parameter evaluated for an image. Furthermore, the patent application discloses a motion detection circuit which compares the extracted parameter values in two images to detect motion of the capsule camera. The controller in the capsule camera system can be configured to operate the capsule camera in an active mode and a monitor mode according to the result of motion detection. However, the patent does not address adjusting the image sensor as additional capsule camera control to conserve storage and/or power consumption.
Another capsule camera system with on-board data storage or wireless transmission was disclosed in the U.S. patent application Ser. No. 12/543,508, entitled “Image Capture Control for in Vivo Autonomous Camera,” filed on Aug. 19, 2009. This application describes an adaptive and dynamic method to adjust the parameter for image capture of a capsule camera with on-board image storage or wireless transmitter. A metric measuring the degree of motion is first computed from a partial frame of current image and a partial frame of a previously captured image. The metric is then compared against a set of parameters to determine a proper action for the underlying image.
While the applications mentioned above use motion detection and motion estimation to eliminate some unnecessary image capture and conserved the precious on-board storage and battery power, it may not fully address other aspects of camera capture control. For example, when there is no motion or little motion detected, images captured do not have to be in full spatial resolution. Furthermore, the luminous energy of the light source may also affect the quality of captured images and affect storage and power consumption requirements, where the luminous energy is represented as a product of the luminous intensity and the exposure time of the light source. It is the goal of the present invention to address these issues of capture control based on motion metric.